1. Field of the Invention
The present invention relates to a digital broadcasting receiver capable of receiving signals of not less than two types of digital broadcasting among digital satellite broadcasting, digital ground wave broadcasting and digital CATV broadcasting.
2. Description of the Related Art
As shown in FIG. 2, a conventional digital broadcasting receiver includes: a tuner 100 for converting a digital satellite broadcasting signal into an intermediate-frequency signal; a tuner 110 for converting a digital ground wave broadcasting signal into an intermediate-frequency signal; a tuner 120 for converting a digital CATV broadcasting signal into an intermediate-frequency signal; A/D converters 200, 200, 200 for digitizing the intermediate-frequency signals respectively sent from the tuners 100, 110, 120; a satellite broadcasting demodulating section 350 for demodulating a digital signal sent from the first A/D converter 200; a ground wave broadcasting demodulating section 360 for demodulating a digital signal sent from the second A/D converter 200; a CATV broadcasting demodulating section 370 for demodulating a digital signal sent from the third A/D converter 200; a changeover switch 450 for selecting one of the signals sent from the satellite broadcasting demodulating section 350, the ground wave broadcasting demodulating section 360 and the CATV broadcasting demodulating section 370; a transport 500 for separating and dividing the signal selected by the changeover switch 450; a decoder 600 for decoding the signal sent from the transport 500; and a CRT 700 for displaying an image of the signal sent from the decoder 600.
The conventional digital broadcasting receiver 5 further includes: a control section 810 for controlling the tuners 100, 110, 120, the changeover switch 450 and the transport 500; a key input section 860 which is one of the setting input sections of the control section 810; and a remote control receiving section 850 for receiving the signals sent from a remote control transmitting unit 900 which is the other setting input section and which is provided separately from the digital broadcasting receiver 5.
For example, as disclosed in Japanese Patent Unexamined Publication No. Hei. 6-54011, a QPSK demodulating circuit of the satellite broadcasting demodulating section 350, by which a pure demodulating function can be exhibited, includes: five multipliers; three filters; a 90xc2x0 phase shifter; a voltage-controlled oscillator; a clock regenerating circuit; two waveform shaper; and a subtracter, wherein all of them can be realized as digital circuits.
Of course, an error corrector, which is the residual function of the satellite broadcasting demodulating section 350, can be also realized as a digital circuit.
On the other hand, although not described in the above publication, the ground wave broadcasting demodulating section 360 is composed of an 8-value VSB demodulator or an OFDM demodulator and an error corrector, wherein all of them can be realized as digital circuits. The CATV broadcasting demodulating section 370 is composed of a 16-value VSB demodulator or a 256-value QAM demodulator and an error corrector, wherein all of them can be realized as digital circuits.
In the above publication, attention is paid to a portion of hardware which is common between the QPSK demodulating circuit and the MSK demodulating circuit, and a method of reducing hardware is disclosed as an invention.
However, in the conventional digital broadcasting receiver 5 composed in the manner described above, the satellite broadcasting demodulating section 350, the ground wave broadcasting demodulating section 360 and the CATV broadcasting demodulating section 370 are required respectively for receiving digital satellite broadcasting, ground wave broadcasting and CATV broadcasting. Therefore, the number of necessary parts is necessarily increased and the manufacturing cost is raised.
When the method described in the above publication is adopted to reduce hardware, it is possible to decrease the number of necessary parts and reduce the manufacturing cost, however, the decrease of the number of necessary parts is limited because attention is paid only to hardware.
It is an object of the present invention to provide a digital broadcasting receiver, the number of necessary parts of which is decreased so that the manufacturing cost can be reduced.
In order to achieve the above object, the present invention provides a digital broadcasting receiver capable of receiving a plurality of types of digital broadcasting, comprising: a software utilizing demodulating section for demodulating a digitized intermediate-frequency signal; a memory for storing software to be used in the software utilizing demodulating section so that each digital broadcasting capable of being received is demodulated; and a control section for giving a command by which the software to demodulate each digital broadcasting is selectively taken from the memory into a memory which is built in the software utilizing demodulating section according to a setting made by a setting input section.